Accessing Databases with Object-Oriented PHP
Illustration by Don Barnett

Submitting multiple queries


From:

Accessing Databases with Object-Oriented PHP

with David Powers

Video: Submitting multiple queries

In my SQL improve, the query and run query methods handle only single queries. If you want to submit multiple queries in a single operation you need to use the multiquery method. This is mysqli_multi.php which you can find in the chapter seven 07_04 folder of the exercise files. We use this to execute three select queries in succession and then loop through the results. To avoid a lot of repetitive typing, I'm going to paste in the code from query.txt, which you can find in the exercise files for this video.
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  1. 13m 33s
    1. Welcome
      1m 4s
    2. What you should know before watching this course
      2m 8s
    3. Using the exercise files
      4m 56s
    4. Setting SQLite permissions
      1m 11s
    5. A quick primer on using PHP objects
      4m 14s
  2. 10m 12s
    1. Overview of PHP database APIs
      4m 5s
    2. Using prepared statements
      4m 24s
    3. Using transactions
      1m 43s
  3. 48m 57s
    1. Creating a database source name
      2m 3s
    2. Connecting to a database with PDO
      7m 27s
    3. Looping directly over a SELECT query
      3m 49s
    4. Fetching a result set
      8m 3s
    5. Finding the number of results from a SELECT query
      7m 14s
    6. Checking if a SELECT query contains results
      3m 32s
    7. Executing simple non-SELECT queries
      6m 2s
    8. Getting error messages
      7m 17s
    9. Using the quote() method to sanitize user input
      3m 30s
  4. 39m 51s
    1. Binding input and output values
      2m 36s
    2. Using named parameters
      9m 51s
    3. Using question marks as anonymous placeholders
      2m 35s
    4. Passing an array of values to the execute() method
      5m 20s
    5. Binding results to variables
      7m 53s
    6. Executing a transaction
      6m 54s
    7. Closing the cursor before running another query
      4m 42s
  5. 21m 20s
    1. Generating an array from a pair of columns
      2m 44s
    2. Setting an existing object's properties with a database result
      4m 42s
    3. Creating an instance of a specific class with a database result
      6m 1s
    4. Reusing a result set
      7m 53s
  6. 38m 14s
    1. Connecting to a database with MySQLi
      5m 57s
    2. Setting the character set
      1m 57s
    3. Submitting a SELECT query and getting the number of results
      4m 4s
    4. Fetching the result
      7m 35s
    5. Rewinding the result for reuse
      3m 20s
    6. Handling non-SELECT queries
      5m 27s
    7. Getting error messages
      5m 47s
    8. Sanitizing user input with real_escape_string()
      4m 7s
  7. 27m 49s
    1. Initializing and preparing a statement
      4m 17s
    2. Binding parameters and executing a prepared statement
      5m 55s
    3. Binding output variables
      5m 6s
    4. Executing a MySQLi transaction
      7m 5s
    5. Dealing with "commands out of sync" in prepared statements
      5m 26s
  8. 24m 7s
    1. Buffered and unbuffered queries
      4m 19s
    2. Using real_query()
      6m 1s
    3. Freeing resources that are no longer needed
      2m 31s
    4. Submitting multiple queries
      6m 41s
    5. Creating an instance of a class from a result set
      4m 35s
  9. 3m 31s
    1. PDO and MySQLi compared
      3m 31s

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Watch the Online Video Course Accessing Databases with Object-Oriented PHP
3h 47m Intermediate Jul 07, 2014

Viewers: in countries Watching now:

Now that PHP has true object-oriented capabilities, it's best practice to access databases using PDO (PHP Data Objects) and MySQLi. These methods produce database-neutral code that works with over a dozen systems, including MySQL, SQL Server, PostgreSQL, and SQLite. Learn how to use PDO and MySQLi to perform basic select, insert, update, and delete operations; improve security with prepared statements; and use transactions to execute multiple queries simultaneously. Author David Powers also covers advanced topics like instantiating custom objects, and compares PDO to MySQLi so you can decide which method is right for you.

Topics include:
  • Connecting to a database with PDO or MySQLi
  • Fetching a result set
  • Executing simple non-SELECT queries
  • Sanitizing user input
  • Binding input and output values
  • Passing an array of values to the execute() method
  • Working with advanced PDO fetch methods
  • Executing a MySQLi transaction
  • Freeing resources that are no longer needed
  • Submitting multiple queries
  • Creating an instance of a class from a result set
Subject:
Developer
Software:
PHP
Author:
David Powers

Submitting multiple queries

In my SQL improve, the query and run query methods handle only single queries. If you want to submit multiple queries in a single operation you need to use the multiquery method. This is mysqli_multi.php which you can find in the chapter seven 07_04 folder of the exercise files. We use this to execute three select queries in succession and then loop through the results. To avoid a lot of repetitive typing, I'm going to paste in the code from query.txt, which you can find in the exercise files for this video.

The new code needs to go after the database connection. So create a new line on line four and paste in the code. Line four defines an array with the names of three car manufacturers. And the rest of the code is a select query to get the minimum and maximum price for cars for the first manufacturer in the makes array. To submit several queries in succession each query needs to be separated by a semicolon, so we need to put that semicolon just before this closing double quote here. So, insert your cursor on line seven between the single quote and double quote and type a semicolon. Then we need to select everything between the double quotes. So that's that semicolon there, and right up to the word select, but not the double quotes. And duplicate that twice. And just make things a little bit tidier, put the select beginning on a new line. And then we need to change the value of makes zero in the second and third one. So this becomes makes one. And this becomes makes two. So what we're doing is we're submitting the same query three times by getting the values from the array up here, Chrysler, Ford, and then Toyota. So we've got three select queries and each one is separated by a semi colon. We can now submit that complete block of code using the multi query method and we'll do that down in the body of the page, here on line 30 inside the else block.

And we simply call the database object, and it's multi-query method, and we pass it the SQL. And this will submit all three queries as a single block, but the results won't be buffered. To get each result set, we need to create a do while loop. So let's put that on the next line. Do, then a block. And after the closing curly brace, we need the while condition. And the while condition needs to check if there are any more results using the next result method of the database object.

So while DB, and then next result. And inside the do while loop, we deal with each result as it's retrieved. To get each result as we go through the loop, we need to call the store result method. So we'll create a variable to store the result. And then call the database object and the store result method. This returns a mysqli result object, so you can treat it in exactly the same way as if you were using query. In this example, each select query is going to return only one row, so we won't need an inner loop inside the dual loop, but we'll just use the fetch us up method to get each row and then display the result.

So, row equals then the result object, fetch assoc and we can then display the results. So, we'll have a double quoted string and we'll have an H2. Because we are using an array element we need to put that inside curly braces otherwise we get a nasty error. So row and then make that closing curly brace. And then, the closing H2 tag and on the next line we’ll create a paragraph.

And we'll format the price using the number format function, so we need to pass that row, min price. And we concatenate more text on the end, to a dollar sign. And format the next one, number_format($row'maxprice'). Just need our closing paragraph tag.

When we get to the end of the loop ,we no longer require the result. So we'll free it using the free method. So result free. And this will now go through all of the results in turn and display them. So let's just save that and test it in the browser. And there are the results from the queries that were submitted in one single operation. So let's just go back and review the code. If we go back up to the top, we have a single block of SQL with three queries in there, each of them separated by a semicolon.

Then we submit it using the multi_query method of the database object. And then create a do while loop. The while condition checks to see if there are any more results using the next_result method of the database object. Inside the do while loop, we store the result using the store_result method, and then you handle it in exactly same way as any other result set. But at the end of the loop you free the memory associated with the results using the free method.

In this example the multi-query method has been used only with select statements but you can use other SQL queries such as insert, update and delete or even a mixture of different types. Just separate each query with a semi-colon. and if only some queries are select statements, use a conditional statement inside the do all loop to check whether store result produces a result set. One other important point, the multi query method does not support prepared statements.

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